Electronic search system

  • US 6,465,982 B1
  • Filed: 07/06/2000
  • Issued: 10/15/2002
  • Est. Priority Date: 01/08/1998
  • Status: Expired due to Term
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First Claim
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1. An electronic search system (1) for a working tool (2), in which system border cable (a) is placed above, under or on ground or floor, so that it separates an inner area (A) within the border cable (a) from an outer area (C), which working tool is intended for attendance of ground or floor, and a first signal generator (3;

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    ) feeds the border cable with current (Ia), whose magnetic field (7) affects at least one sensing unit (8) located on the working tool (2), so that the at least one sensing unit (8) emits signals (9) to a control unit (10), which in cooperation with an engine control (11), or a signal system for a driver, and at least one driving source (12, 13) directs the tool'"'"'s motion in order to prevent it from remoting from the inner area (A), wherein the first signal generator feeds the border cable with current (Ia) containing at least two alternating-current components (14, 15) of different frequency, and the components (14, 15) are lying in a known relation of time to each other, and at least one more cable, called search cable (b, d, e) is placed at least partly within the inner area (A+B+D+E), so that it separates at least one search area (B, D, E) within the inner area, and each search cable (b, d, e) respectively is fed by a signal generator (3, 4, 5) with an adapted current (Ib, Id, Ie), whose altemating-current components (14, 15) are virtually identical with the altemating-current components in the border cable (a), but where the direction of flow, at least for the alternating-current component (15) with the higher frequency, in each one of the search cables is alternating in time in being either in phase or out of phase in relation to the current flow direction in the border cable (a), so that the magnetic fields in the different areas (A, B, C, D, E), which are separated by each cable respectively, are forming at least three essentially unique timer patterns, and hereby the control unit can evaluate the difference in the signals (9) caused by the magnetic field'"'"'s different time patterns in the inner area (A), the outer area (C) and at least one search area (B, D, E), and the control unit can therefore emit an area signal (16), which mainly takes up one of at least three states depending on the position of the sensing unit (8) in relation to the border cable (a) or each search cable (b, d, e) respectively.

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